This invention relates to a method of restraining a belt wearer in a vehicle in the event of a collision by means of a safety belt. The invention also relates to a device for such a safety belt.
By the use of safety belts, normally of the three-point type, personal injuries resulting from frontal collisions have been reduced. With the aim of reducing the risk of injury still further, it has become common to ensure that the safety belt tightens at the moment of impact, so that the wearer is not thrown with unnecessary force against a slack safety belt. This is achieved by means of a belt tensions being activated when the retardation of the vehicle reaches a predetermined value, normally about 5 g. Such belt tensions are usually mounted at the side of the person, where the shoulder strap and the lap strap meet at the belt fastener, and provide primarily a tightening of the lap strap, but also of the shoulder strap. In other embodiments the belt tensions acts upon the top end of the shoulder strap and thereby provides greatest tightening of the shoulder strap, while the tightening of the lap strap is less.
However, experience has shown that in spite of these measures, in the event of a collision, the contact with the shoulder strap can cause chest injuries, particularly in elderly persons. The safety belt protects the wearer from hitting the vehicle, but the wearer can still be injured by the safety belt itself. With the aim of reducing this type of risk of injury, tests have been carried out of different ways of limiting the load on safety belts. For example, one solution has been to use thinner webbing near the upper fixing point so that the safety belt will yield somewhat at a certain load. With the same aim the belt roller can be mounted at a fixing point which yields at a certain load. Another solution is that the belt roller is connected with a friction coupling which can be set to absorb various degrees of load.
Common to all of these known solutions is the fact that the upper body of the belt wearer is allowed to move forwards an appreciable amount during the extending of the safety belt. The stresses on the belt wearer are reduced, but it would be desirable to be able to reduce the stresses and thereby the risk of injury to the belt wearer still further.
The aim of the invention is to further reduce the risk of injury to a belt wearer in the event of a collision. A further aim is to achieve this in a simple and reliable way using simple means.
According to the invention, by means of tightening the safety belt for at least 300 ms and during this time limiting the maximum pull on the safety belt to a predetermined value, an effective yet gentle restraint of the belt wearer is achieved. The tightening can advantageously continue for 800 ms or more in order to ensure good restraint during a relatively long-lasting collision.
A device according to the invention is so constructed that the tightening device can operate for at least 300 ms and in addition the load-limiting device is arranged to operate between the spooling device and the tightening device. By this means tightening can take place continuously with simultaneous load limitation, so that the belt wearer is restrained gently and effectively.
According to a particularly advantageous variant of the invention, the tightening is carried out in a part of the safety belt which passes over the shoulder of the belt wearer.
The restraining of the belt wearer can be improved still further according to the invention by means or commencing the tightening with a certain pre-warning before the collision.
Further characteristics and advantages are evident in the following description and patent claims.